Both plastic and metal closures for various bottles and containers which include a tamper-evident feature have been known for many years. In most cases, the tamper-evident feature comprises a lower shoulder or skirt portion which is intended to be separated or fractured from the remainder of the closure upon removal of the closure from the container so that it becomes evident that the container has been opened. In the past, the majority of such types of closures have been predominantly made of metal; however, the use of metal has resulted in significant problems, which relate primarily to the fact that removal of the closure does not result in a clean and efficient fracture of the lower skirt portion. Also, in some instances, sharp edges are created that cause danger to the user.
In connection with plastic closures of this type, again, a large number have been patented in the past. Exemplary of one type of closure is shown in U.S. Pat. No. 4,033,472. The closure in this patent requires a two-step application procedure which includes the initial application of the closure to the bottle, followed by a heating process whereby the lower depending bead is deformed against the surface of the bead or collar on the bottle itself.
When the cap closure is formed of a plastic material, the liner normally applied to the inner surface of the closure is generally eliminated and a sealing means is formed integral with the bottom surface of the circular top wall. Many of the linerless closures available commercially rely upon deflection of a flexible fin depending from the top wall of the closure. The lateral flexing movement of the fin tip is designed to cause the tip of the fin to move into sealing engagement with an edge of the container finish. However, this created problems in that the sealing portion of the closure will lose its elastic memory after storage for a period of time and then tends to reduce the sealing force. Thus, the seal may be lost.